Photographic heat developable elements and processes have been described in U.S. Pat. Nos. 3,152,904, 3,180,732, 3,301,678, 3,392,020, 3,457,075, 3,531,286, 3,761,270, 3,764,328, 3,985,565, 4,022,617, 4,507,380, 4,536,467, 4,584,267, 4,590,154, 4,595,652, 4,770,989, 4,847,188, and 5,032,499, in United Kingdom Patent Nos. 1,131,108 and 1,167,777, and in Research Disclosure, Nos. 12044, 12533, 15108, 15127, 16479, and 17029 (pages 9-15, June 1978).